When adding a torrent to ktorrent, the dialog that pops up tells you how much space is required for the torrent, how much space is available in the currently selected directory/disk, and how much space will be available on that disk afterwards. It also tells you how many of the files in the torrent are already on disk. However, it does _not_ take into account the size of those files on disk when calculating how much space will be available after the download. I'd very much like it to.

Since it's already checking whether the files are there, it wouldn't be much more work to get their sizes while it's at it. It could then add those up and subtract that amount from the "After download" number. That way, you won't get situations where you already have most or all of a torrent on a disk but "After download" is claiming that there isn't enough space on the disk, because the torrent's files would take up more space than is left on the disk if they weren't already on the disk.